1. Field of the Invention
This invention relates to processes for obtaining valuable fuel products from coal, and more particularly, relates to the integration of coal liquefaction and coal gasification so as to obtain a wide range of selected coal-derived fuel products. Specifically, the invention relates to the processing of coal or other solid fuel products in which coal liquefaction and coal gasification are combined with a methanol-to-gasoline conversion process to produce a wide product slate of fuels.
Coal is becoming an increasingly attractive source for gaseous and liquid fuel inasmuch as coal is available in abundant supply and can be liquefied by a variety of techniques to produce a range of gaseous, distillate and nondistillate coal products. It is recognized that the coal products derived from liquefying coal may be refined and furnish a substitute for petroleum-based fuels and/or petroleum-based feedstocks for the chemical industry.
It has also been well established that coal can be converted to gasoline by gasification of the coal and the subsequent production of methanol from the synthesis gas which is produced followed by the catalytic conversion of the methanol to gasoline. A ZSM-5 type zeolite catalyst has been found to be very effective in the conversion of methanol to gasoline. However, if a wide range of distillate products is desired from coal, the methanol-to-gasoline conversion process alone is not sufficient. Accordingly, a need exists to provide a wider product slate from coal than is ordinarily obtained from the methanol-to-gasoline conversion process. In accordance with the present invention, a wider product slate is obtained from coal by integrating the methanol-to-gasoline conversion process with coal liquefaction and coal gasification. A very flexible, material and energy efficient coal conversion process is provided which allows greater selectivity as to the fuel products derived.
2. Description of the Prior Art
Deriving a gaseous and liquid fuel from coal utilizing integrated coal liquefaction and coal gasification is known to the art. For example, an integrated process for deriving fuel from coal is disclosed in an article entitled "Development of A Process for The Supercritical Gas Extraction of Coal" by J. C. Whitehead, National Coal Board, Coal Research Establishment, Stoke-Orchard, Cheltenham, England, 1979. In the article is described a process for deriving fuels from coal which includes the supercritical gas extraction of coal in which the extraction process is based on the ability of compressed gas to dissolve significant quantities of a high molecular weight substrate. The coal extract can be further upgraded. The article reveals that a variety of process options, in terms of processing routes and product slates have been evaluated and that the majority of these options are based on the principle of generating power, process heat, and hydrogen from the residual solid char which remains after coal extraction. Any char excess to requirements in the schemes is converted to synthesis gas. Solvent make-up for the supercritical gas extraction can be obtained from the products of extract upgrading.
U.S. Pat. No. 4,191,700 issued Mar. 4, 1980 to Lebowitz et al, discloses a process for upgrading fuels, particularly coal, by means of integrating coal liquefaction and coal gasification with methanol synthesis. In this patent, coal is solvent refined with a conventional hydrogen donor solvent under severe conditions, preferably in a hydrogen environment, to convert substantially all the coal to a liquid product which is divided in a vacuum still separation zone into a light distillate product, recycle solvent, a heavy distillate, and a vacuum residue slurry. The vacuum residue slurry provides an efficient feed for a partial oxidation gasifier which produces synthetic gas as a feed for methanol and/or methane production and to supply hydrogen, as required, to the liquefier.
Although integrated coal liquefaction and coal gasification, as described above in the Whitehead article and Lebowitz et al patent, is known and is used to derive a wide slate of fuel products from coal efficiently and with increased product selection, the integrated coal liquefaction and gasification processes up to the present time have not fully utilized the synthesis gas products which are formed during coal gasification which follows coal liquefaction so as to further increase the production of high value fuel products and optimize the ability to select which products are to be obtained from the coal. As set forth in the integrated process as discussed above, the solid char which remains from the supercritical gas extraction in the Whitehead article is gasified to produce a synthesis gas while the vacuum residue slurry described in Lebowitz et al is separated from the liquefied coal and converted to methanol or methane. These end products are apparently used in the respective processes to provide heat for the process in which excess products will be sold for heating value.
U.S. Pat. Nos. 4,222,845 and 4,222,846 issued Sept. 16, 1980 to Schmid are typical of integrated coal liquefaction-gasification processes in which the synthesis gas which is formed is burned as fuel within the process so that the heat content is recovered via combustion. Any excess synthesis gas which cannot be utilized as fuel within the process is subjected to a methanation step or methanol conversion step to increase the heating value of the synthesis gas.